Chromium complex compounds



Patented Apr. 8, 1947 UNITED STATES PATENT OFFICE CHROMIUM COMPLEX COMPOUNDS Edwin A. Robinson, Chatham, and Ralph M. Beach, Newark, N. J., assignors to National Oil Products Company, Harrison, N. J., a corporation of New Jersey No Drawing. Application November 21,1941,

Serial N 0. 419,912

Claims.

pally in the production of heavy leathers such I as sole leather. As the rate of diffusion of Vegetable tannin into skin is very slow and consequently a long time is required to completely tan heavy leathers with the vegetable tannins, many attempts have beenlmade to speed up this process. One method that has been proposed involves the use of concentrated tanning liquors, However, if hide is put directly intoconcentrated tanning liquors, the rate of combination of the tannin with the skin protein is very likely to be abnormally great compared to the rate of diffusion of the tannin into the interior of the skin; consequently the outer layers of the hide are drawn or contracted to a greater extent than the inner layers, whereby distortion of the outer layers with respect to the inner layers is effected, thus greatly detracting from the appearance and value of the leather.

In order to overcome such difiiculties, tanners have found it necessaryto adopt a stepwise process when tanning with vegetable tannins. By such a process they treatthe skins first with a tan liquor which has already been used to tan a large number of skins and in which, consequently, the ratio of nontannin to tannin is very but also he is forced topurchase'the skins many i months before hewill be able'to sell them as finished leather. Thus with varying market conditions, a great amount of uncertainty and speculation enters into the tanners business. Also,

in order to maintain a certain output of leather,-

he must maintain manytimes, the amount of equipment which he wouldhave to have to pro ducethe same amount of leatherif the tanning could. be accomplished by someshorter and simpler method, Becausetof these andother. inhen cut disadvantages of the aforementioned procedure, the manufacturers net profits are much less and the cost of the finished leather to the consumer much greater than if a more efficient process were available for producing first-class vegetable tanned leather. H

The volume of the collagen fibers in the skin increases as more tannin combines therewith; and in themanufacture of a leather where great solidityjis required, such as, for example, in sole leather, it is not suificient merely to convert all of the collagen into leather; and in orderto get the maximum fullness and solidity the hides,

after all of the collagen has been converted to leather, are treated with very. concentrated tan ning liquors so that the maximum amount of tannin will be fixed. Thus in such casesthe process is even more cumbersome and costlythan that as set out hereinabove.

Chrome tanning processes take much less time than vegetable tanningprocesses, andat the present time most of the worlds supplytof light leathers is tanned 'by means of chromium salts. However, in the case of heavy leathers, chrome tannage will not produce the degree of plump.- ness and fullness which the trade demands. ,In chrome tanned leathers the individual fibers are usually thin as in dried, raw skin, but in vegetable tanned leathers, the fibers are much larger and in most cases they almost completel fill the interfibrillary spaces, thus giving a very desirable full and plump leather.

In addition to the shorter time required for tanning by the chrome processes, such processes also have the advantage of producing leather possessing a much higher temperature of gelatinization than can be. obtained in leather through vegetable tanning. The term temperature of gelatini'zation is used herein toiconnotethat temperature at which the tanned leather shrinks or shrivels when subjected to elevated temperatures. The temperature of gelatinization is a relative measure of the reaction of the tanning agent upon the skin protein causing the latter to Withstand or toleratevarious degrees of temperature without harm. Leather properly tanned with chromium salts can usually be kept in boiling water for 5 minutes or longer Without showing any signs of curling. In other words, the leather has a temperature of gelatinization of C. or higher. However, in the case of vegetable tanned leathers, it is very difiicult to obtain a temperature of gelatinization of much over 84 C. to 86 C., and in many cases the resulting value is below 84 C.

Attempts have been made to combine chrome tannage with Vegetable tannage. In such cases the leather is first treated with chrome tanning liquors and then given a surface tannage with vegetable tanning liquors. In some cases and for some purposes leather which has been so treated was tolerably satisfactory, but in many cases and for many purposes it was by no means as satisfactory as straight vegetable tanned leather.

In view of the aforementioned and other various limitations and'disadvantages of both chrome and vegetable tanning, and combinations thereof, much work has been done in attempting to develop new and improved tanning agents and processes for using the same. One of the pioneers in this field was Stiasny, who presented to the world a new class of materials which he called syntans. He had produced what were apparently condensation products by mixing and heating phenol sulfonic acids with formaldehyde in an acidsolution. He obtained water-soluble products which he claimed possessed marked tanning properties. However, the syntans produced by Stiasny and similar products produced by other investigators have had no filling or plumping properties,

and when used for tanning they give an undesirable thin and empty leather. Moreover, leather produced by the use of such syntans has exhibited a very poor temperature of gelatinization value usually runnin in the order of about 60 C. to 70 C. as compared to about 80 C. to 86 C. for vegetable tanned leather and 100 C. or over for chrome tanned leather. To increase the temperature of gelatinization of syntan tanned leather, various investigators have suggested adding chromium salts to the syntans. In some cases chromic salts have been added and in some cases chromate compounds, but when the chromate salts, such as sodium dichromate, are added, they 'are invariably reduced to the chromic state with the concurrent oxidation of the syntan, thus producing quinone groups on the aromatic nuclei and converting the methylenic linkages of the condensation roducts to carbonyl groups. In all cases the chromium is apparently present as a positively charged ion, as evidenced by the fact that it may be precipitated with excess strong alkali.

The presence of chromium in the form of a positively charged ion along with carbonyl and ketone groups apparently tends to cause a shrinkage of the surface of the leather which is, of course, detrimental to the leather and depreciates the value thereof. It is not definitely known what is responsible for this; however, there is 'a possible explanation for such a result. It is to be understood that the explanation that we advance herein a theoretical one, but it does seem quite plausible.

ignated by the general formula It is known that the hydrogen of the carboxyl group tends to shift over to the amino group,

leaving the carboxyl group with a negative charge and giving the amino group a positive charge,

whereby the general formula would then be As chromium is usually present in tan liq in the form of a positively charged ion, it apparently combines with the negatively charged carboxyl group. As chromium does form a very stable compound with leather, it seems very likely that it has chemically combined with the protein in some such manner as we have set out. In

7 vegetable tanning liquors, however, the active tanning agents, according to the Procter-Wilson theory, apparently are negatively charged, and thus combine with the positively charged amino groups of the skin protein. It is also known that vegetable tanning agents contain numerous aldehyde and ketone groups, and therefore it is also possible that a chemical combination may be effected between the amino groups of the protein and the aldehyde and carbonyl groups of the vegetable tanning agents in some manner, such as, for example,

In any case it does seem apparent that the Vegetable tannins combine in some manner with the amino groups of the skin, whereas the chromium in chrome tanning agents probably combines with the carboxyl groups of the skin.

In synthetic tanning agents which have been prepared as noted hereinabove by subjecting sulfonated condensation products of phenolic aromatic compounds to oxidation with hexavalent chromium, there are, as already mentioned, both quinone and carbonyl groups, which may combine with the amino groups of the hide; and positively charged chromium in the trivalent state, which apparently combines with the carboxyl groups of the hide. Since such is the case, it seems possible, therefore, that this two-fold action tends to draw the difierent constituent groups of the skin more closely together, thus causing undesirable shriveling and shrinking of the leather.

However, whether our theory is correct or not, it is known that the aforesaid synthetic tanning agents have not functioned satisfactorily in leather tanning processes. The use of the syntan brings about the undesirable result of shrinking the leather.

whereby the time required for the tanning of leather by vegetable tanning processes may be materially decreased. As aforementioned, in most cases from two to three months are required to complete the usual vegetable tanning of heavy leathers, whereby the processing costs remain exceedingly high.

It is the object of this invention'to obviate the foregoing and other disadvantages inherent in the tanning of leather.

It is also the object of this invention to provide new and improved synthetic tanning agents.

A further object of the invention is to provide improved synthetic tanning agents, which will T produce leather-which is plumpgsoft and has a desirable color and a high temperature of gelatinization. Another object of the invention is to provide synthetic tanning agents which may be used to pre-tan leather, and which when so used will materially lessen the time required tothereafter thoroughly vegetable tan said leather.

An additional object of the invention is to provide an improved process of tanning leather whereby the time required is materially decreased.

Other objects of the invention will in part be obvious and will in-part appear hereinafter.

It has now been found that the foregoing and other objects of the invention may be accomplished by treating a sulfonated aromatic compound or a condensation product thereof with a compound containing hexavalent chromium, in such almanner that the chromium or the major part thereof will be reduced to trivalent chromium, but so regulating the conditions and quantitles of materials that instead of chromium being present in the'finished product in the form of 'a' positively charged ion; it 'will be present in a negatively charged complex ion; and byusing tanning agents so produced in a manner asset out hereinafter.

According to Werners coordination theory, as set out in his book Neure Anschauungen auf dem Gebieteder Anorganischen Chemie, certain atoms tend to draw to themselves, in the form of surrounding shells and by forces other than primary valence, anumber of other atoms or coordinated groups. The central atom with its coordinated groups constitutes a nucleus outside of which are located the atoms or radicals which are held to the rest of the molecule by primary valence forces. The coordination number of an element indicates the number of groups which an "atom canhold in this surrounding shell. Chromii m happens to be one of the metals Whose atoms have this power to combine with other atoms, not only b means of their recognized primary valence forces, but also by. means of theseso-called auxiliary valencies. The majorby the addition of silver nitrate, and according to Werners theory its structural formula is:

H H20 n20 or H20 301- The water molecules are thus coordinately bound to the chromium. atom while all. three of. the chlorine atoms are. combined with thechromium nucleus by means of. primary valence forces,

and in this-state they are readilyiprecipitatable bysilverions. y

"The 18 form. of chromic chloride ,1 is; a green salt of the formula CrClsbI-lzO. Onlytwo-thirds of its chlorine is precipitated from solution by silver nitrate which indicates thatonly two of the chlorine atoms are boundto the chromium nucleus by primary valence forces and. that the third is now contained Withinthe nucleus. Thus theformula would be:

When the one chloride ion" penetrates into the nucleus it displaces one of the water molecules; and as the chloride ion is negatively charged, it neutralizes one of the three positive charges on the nucleus. When it does this, the chloride ion ceases to be an ion any longer, but now forms part of the complex which constitutes the nucleus, and it is incapable of being precipitated by silver ion.

In the ca form of chromic chloride, two chlorideions have penetrated into the nucleus thus displacing two of the coordinately bound water molecules to give the formula CIC13.4H2O, which maybe depicted structurally as follows:

The two chloride ions have neutralized two ofthe three positive charges on the nucleus and thus ceased to be ions any longer and have become a part of the nucleus. The nucleus now has only one positive charge, and only one chloride ion is left capable of precipitation by silver nitrate. l

By suitably varying the conditions, it is possible to replace all of the coordinately bound water molecules with chloride ions and thus obtain .a nucleus having three negative charges. Thus, for example. it is possible to obtain a chromium compound such as sodium hexachloroe chromiate whose structural formula would be:

c1 c1 [c1 c1- c1] c1 01 Thus the chromium is now present in a negatively charged complex ion, and all of the chlorine atoms are attached to the central chromium atom by non-ionized links.

The chlorides of chromium have been used here merely to illustrate Werners theory. Chloride ions are not the only ions that may so penetrate into. the nucleus; a great many other atoms or radicals will also penetrate into the nucleus and become bound by non-ionized links. In fact even molecules may do this as we have already seen in the case of the hydrated chromic chlorides where molecules of water are contained in-the nucleus. When cations penetrate into the nucleus, they either increase the positive charge on apositively charged complex or decrease the negative charge on anegatively charged nucleus; while anions entering the complex either decrease the positive charge or increase the negative charge of the nucleus. r

We have found that by treating certain sulfcnated aromatic compounds with hexavalent chromium in such a manner that the sulfonated compound will be partially oxidized, and the hexavalent chromium reduced to trivalent chromium, and negatively charged complex chromium ions formed instead of positively charged chromium as is the usual case, very efficient tanning agents result which when used totan hides will produce a very desirable leather, Furthermore, if hides are given a pre-tan withsuch tanning agentathey may then be treated'immediately with concentrated vegetable tanning liqucrs whereby vegetable tanned leather of very higheuality is produced.- By such a process vegetable tanned heavy leather may now be produced in from ten to twelve days. Moreover, the leather resulting from this process is superiortothat produced in from sixty to ninety days by theordinary. known vegetable tanning methods. .In addition to the shorter length of time required for Ellio :the tanning and the leather having all the desirable qualities of the usual vegetable tanned leather, the leather also possesses many of the highly desirable qualities of chrome tanned leather, 6. g. a high temperature of gelatinization.

In preparing the synthetic tannin-g agents of our invention, various sulfonated aromatic compounds may be reacted with hexavalent chrmium-containing compounds. Thus we have found that highly efiicient tanning agents may 'beprepared by treating with hexavalent chromium compounds either sulfonated cresols, such as sulfonated ortho, meta or para-cresol or mixtures thereof; sulfonated phenols; other sulfonated hydroxy aromatic compounds, such as sulfonated beta naphthol and sulfonated gallic acid; sulfonated alkylated aromatic compounds, such as sulfonated diarnyl naphthalene, sulfonated mono amyl phenol, sulfonated mono-lauryl benzene, etc.'; sulfcnated aromatic aldehydes or ketones such as benzaldehyde and 4,4 dihydroxy benzop'henone, etc. or sulfonated condensation products of any of these aromatic compounds with formaldehyde.

Any suitable hexavalent chromium containing compound may be used to treat the sulfonated aromatic compounds, although, of course, the more convenient forms, such as sodium dichromate and potassium dichromate, are highly preferred, In order to produce the synthetic tanning agents of our invention, it is very important that the conditions under which they are prepared be carefully controlled, and that the proper proportions of materials be used.

We .are aware of British Patent No. 145,167 and its disclosure relating to the production of synthetic tanning agents by the oxidation of sulfonated condensation products of hydrocarbons or phenols. In producing their products the patentees state that they continue the oxidation of the condensed materials until the materials give no color reaction with ferric chloride, which shows, ofcourse, that whether the parent materialwas a phenol derivative or a hydrocarbon demanganate, perchlorate, perborate, chlorine, ni-

tric acid, potassium bichromate, etc. The pat- .entees further state that they obtain insoluble products in many cases and that they therefore have to mix the/products with other materials to bring them into solution. for use in the tanning operation.

, Thu it can easily be seen that the tanning agents of British Patent No, 146,167 are merely highly oxidized sulfonated condensation products of cyclic hydrocarbons or phenols, and that any .of a large number of oxidizing agents may be used to bring about the oxidation of the condensation products, Since any of a large number of oxidizing agents may be used, it is clearly apparent that the oxidizing agent itself has little importance as far as actual tanning is concerned, but that instead it is the oxidized product which produces the tanning effect of the materials obtained. Potassium dichromate is listed as one of the oxidizing agents that may be used, but apparently its sole action is to oxidize the condensation products. It does not appear that when the potassium dichromate is used as the oxidizing agent that.

any complex chromiates are produced, such as We obtain by our invention. Apparently the chromium which is'reduced in the oxidationture as positively charged chromium ions, To determine whether such Was the case or whether the chromium was present as negatively charged ,chromiate, we prepared products in accordance with the procedure set out in Example 'IIof this British patent. These products had a greenish color and when an excess of caustic alkali was added to an aqueous solution of the resulting materials, a precipitate of chromium hydroxide was obtained, which clearly indicates that the reduced chromium was present as the positively charged ions. If the chromium had all been present as negatively charged chromiate, no precipitate would have resulted on the addition of the excess alkali.

We have found that in order to obtain the .desired chromiate ions and to prevent the formation of insoluble products such as are obtained by the process of British Patent No. 146,167, much less dichromate must be used than is used in the aforesaid British patent. Also we have found that much better products are obtained if the aromatic compounds are first condensed with formaldehyde before they are treated with the dichromate.

In preparing condensation products of the sulfonated aromatic compounds, we have found that as much as three moles of formaldehyde per mole of the. aromatic compound may well be used; however, in mostcases we prefer to use one-half mole of formaldehyde per mole .of the sulfonated aromatic compound. It is important thatthe temperature, time and other conditions be con.- trolled so that the condensation does not proceed to the point where insoluble resinous products are obtained. We prefer to cool the sulfonated aromatic material to a temperature below room temperature, and then add a solution of formaldehyde thereto and allow the mixture to stand overnight at room temperature, during which time the formaldehyde will condense with the sulfonated aromatic compound without forming insoluble material. A very convenientway in which to cool the sulfonated aromatic compounds before adding the formaldehyde is to add sufficient ice to the sulfonated material to cool it to the desired temperature. The condensation may be carried out in a shorter time if it is done at higher temperatures; but when higher temperatures are used, some insoluble materials are more likely to be produced than at the lower temperatures. Consequently greater care must be taken than is necessary in the preferred procedure. i

In treating the sulfonated aromatic condensation products with dichromate, we have found that if more than one-fourth mole of dichromate (3 equivalent weights of chromium) per mole of sulfonated aromatic substance is used, undesirable insoluble material is usually formed. 'We prefer to use not more than one-eighth mole of dichromate (l /2 equivalent weight of chromium) per mole of the sulfonated aromatic compound, since usually better products will be obtained than with the larger amounts of dichromate. If desired, even smaller quantities of dichromate I may be used. Thus we have found that excellent 9: C. to C. while adding the dichromate and for a short time thereafter, and then the temperature of the mixture is allowed to rise to room temperature and maintained at that temperature overnight before neutralizing the excess sulfuric acid. The dichromate is preferably added as a 5 aqueous solution. In neutralizing the excess sulfuric acid, care must be taken to add the alkali slowly and with stirring in order to prevent the formation of lumpy particles in the mass. It is preferred to use from a 15% to a NaOH solution to neutralize the excess. acid, although other bases may be used if so desired. Enough alkali is added so that a 2% aqueous solution of the end product will have a pH between about 3 and 6. The products of our invention may be used in the tanning of leather just as other tanning agents are used. They are particularly applicable, however, to the pretanning of heavy 1eather,such as sole leather. Leather pretreated in thismanner may then be vegetable tanned in from 10 to 12 days where ordinarily several months would be required to givethe heavy leathers a complete vegetable tannage.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following examples which are given merely to further illustrate the invention and are not to be construed in a limiting sense, all parts given being by weight:

Example I 108 parts of cresylic acid were heated with 110 parts of sulfuric acid at a temperature of 120 C. for .two hours. 40 parts of ice were added followed by the slow addition at a temperature below 25 C. of 50 parts of formalin (37% formaldehyde) After standing overnight, 40 parts of sodium dichromate dissolved in 80 parts of water were added very slowly, keeping the temperature below 10 C. After 3 hours at 10 C. the temperature was allowed to rise slowly to room temperature and was then maintained at that temperature overnight. The next day the mass was neutralized with caustic soda and adjusted to a suitable pI-I. The resulting product had a reddish brown color. Kid skin tanned with this product gave a temperature of gelatinization test of about 100 C. as against 84 C. for quebracho tanning solution.

Example II A very good tanning agent was produced by treating a condensation product of sulfonated cresol with sodium dichromate the same as in EX- ample I, the only difference being that twice as much sodium dichromate per mole of cresol was used in this case than was used in Example I. The resulting product had a reddish brown color. On' adding excess sodium hydroxide to a dilute solution of the product, no precipitate was obtained which clearly indicates that the reduced chromium was not present as positively charged ions. I

Example III 282 parts of phenol and 300 parts of 20% oleum were heated at a temperature of 100 C. to 120 C. for one hour, and then cooled to room temperature and kept at that temperature over the weekend. To 146 parts of the resultin product there were added 75 parts of ice and sufficient formalin to give a concentration of 0.5 mole of formaldehyde per mole of phenol. After standing overnight, this was neutralized with sodium hydroxide to a pH of 5.0. The resulting product washeated under vacuum to remove any excess formaldehyde and was then treated with sodium dichromate similarly as in Example I using one-- sixteenth mole of sodium dichromate per mole of phenol.

I Example IV Sulfonated phenol was condensed with formaldehyde and oxidized with dichromate as in Example III, the only difference being that one mole of formaldehyde per mole of phenol was used instead of one-half mole of formaldehyde per mol of phenol as in Example III. Both the product of Example III and the product in this example were very good synthetic tanning agents. In both cases leather tanned therewith had a temperature of gelatinization of over C.

From the above description and examples, it can readily be seen that We have produced novel synthetic tanning agents. These syntans apparently contain chromium in the form of a negatively charged ion or chromiate. They apparent ly react with the skin collagen to form leather in much the same way as vegetable tanning agents. Not only do they have the desirable features of vegetable tanning agents, but also those of chrome tanning agents, and thus they are well adapted to tanning various types of leather. In addition they are excellent pretanning agents, and heavy leather which has been pretanned with them may be given a complete vegetable tannage in from ten to twelve days, whereas several months would be ordinarily required for usual vegetable tanning.

The exact chemical structure of the tanning agents or the exact mechanism by which they are formed has as yet not been definitely deter-' mined. However, we believe that negatively charged constituent groups or possibly a whole molecule of sulfonated material bearing a negative charge penetrates into the chromium complex, thus giving it a negative charge as a result of which the chromium will not be precipitated when excess alkali is added to the product. However, it is possible that the negativecharge may not be due entirely to the sulfonated aromatic compounds or the condensation products thereof, since the reaction is carried out in the presence of sulfuric acid, and sulfate radicals may thus penetrate into the chromium complex and contribute to producing the negative charge thereon.

Furthermore, the charge on the nucleus may vary" from a minus one to a minus three since one or two molecules of water may be within the nucleus.

Thus when a monovalent base such as sodium hydroxide is used to neutralize the reaction mass, the syntans have the following general formula:

wherein Cr stands for trivalent chromium, A.S0s

Whenever p is more than 1, A.SO3 may represent still larger compounds.

11 more than one specific aromatic sulfonate; e. g. if p is 2, one A503 may be a sulfonated cresol and the other-'AISOs may be a formaldehyde condensation product of a sulfonated cresol; if p is 3, one A.SO3 could be a sulfonated cresol, and the other two could be formaldehyde condensation products of sulfonated cresols; etc. It will be noticedthat in every case the complex ion has a negative charge of at least one, and that there is at least one A503 group in each complex ion. From inspectionof the general formula, it will'be seen that there may be either one or .two S04 groups present in the complex ion or there may be none at all; likewise with the water molecules. If 'a sulfonated cresol, part of which-has been condensed with formaldehyde, is reacted according to the process of our invention with sodium dichromate in the presence of sulfuric acid and the reaction mass neutralized with a sodium alkaline agent, such as sodium hydroxide,,synthetic tanning agents may be obtained having a formula such as one of the following:

(formaldehyde condensation, product of sulionated cresol);

' (sulionated cresol);

'- (formaldehyde condensation product of sulfonated cresol; .3Na+ Ofcourse there are many variations of the general formula given above which may be formed.

Large and complex molecules may thus be built up andgive the syntans the filling properties which are desired. It is also-known that under certain conditions two or more chromium complexes are united .by a linkage containing both primary and coordinate valence and thus form This is known as 01111- cation and itis very possible that such may be taking place in the formation of our tanning agents andmay partly be the reason for their desirable filling properties.

Since certain changes in carrying out the above process and certain modifications in the composition which embody the invention mayb made without departing from its scope, it is intended that all matter-contained in the above description shall be interpreted as illustrative and'not I in a limiting sense.

,Having described our-invention, what we claim as new and desire to secure by Letters-Patent is:

l. A process for the production of'a chromium complex compound incapable of precipitating chromium upon an addition of an excess of alkali thereto which "comprises cooling a phenol sulfonate below room temperature, condensing formaldehyde therewith in the ratio from /2 to3 mols of, formaldehyde to each mol of phenolsulfonate, and reacting hexavalent chromium compound withthe sulfonated phenol formaldehyde "con densation product, the ratio of equivalent weights of chromium in the hexavalent chromiurn'compound to mols of phenol formaldehyde codensation product being not more than 3 to 1.

2. A processfor the production of a chromium complex compound incapable of precipitating chromium upon an 'additionof anexcess of alkali thereto'which comprises coo-ling cresol sulfonate below room temperature, condensing formaldehyde therewith in the ratio from to 3 mols of formaldehyde to each mol of cresol sulfonate, and reacting hexavalent chromium compound with the sulfonated cresol formaldehyde'condensation product, the ratio of equivalent weights of chromium in the hexavalent chromium compound to'mols of cresol formaldehyde condensationproduct being not more than 3to 1.

3. Aprocess which comprises cooling phenol sulfonate below room'temperature, condensing formaldehydetherewith inthe ratio from 'to 3 mols of formaldehyde to Leach mol ofphenol sulfonate, and reacting hexavalent chromium compound with the sulfonated phenol formaldehyde condensation product, the ratioof equivalent weights of chromium in the hexavalent chromium compound tomols of phenol formaldehyde condensation product being not morev than 3 4. A process which comprises cooling aphenol sulfonate below room temperature, condensing formaldehyde therewith in the ratio of from to 3 mols of formaldehyde to each mol of phenol sulphonate, and reacting awater 'solub le dichromate with the sulfonated phenol formaldehyde condensation product, the'mol ratio of-the-di-w chromate tothe phenol formaldehyde condensation product being not more than 1 to 4, 5. The product of the process of claim 1.

EDWIN A. ROBINSON; RALPH M. BEACH.

REFERENCES CITED The following references are-of record inthe file dfthis patent:

ITED STATES PATENTS OTHER REFERENCES Mellor, Inorganic and Theoretical Chemistry,

voljXI (1931), pages 400-409 881-886. 

